Current limiting sparkgap with means for regulating gap voltage

ABSTRACT

A surge voltage arrester, such as a lightning arrester, is provided with a sparkgap assembly having a plurality of matched pairs of arc-confining chambers that are operable to regulate movement of arcs formed within the chambers of the assembly to prevent the assembly from developing undesirably high peak voltages when a surge voltage is discharged through it, and also to maintain the arc-quenching voltage rating of the assembly at a substantially constant value following repeated surge current discharges. A narrow passageway is provided between each of the matched pairs of arc-confining chambers in order to allow smallcurrent arcs to move between the two chambers while confining large-current arcs to a single one of the chambers, thus, one of the chambers is protected from exposure to destructive erosion and contamination by large-current arcs.

United States Patent 51 May 16, 1972 Miske, Jr.

[54] CURRENT LIMITING SPARKGAP WITH MEANS FOR REGULATING GAP VOLTAGE,

[72] Inventor: Stanley A. Miske, Jr., Pittsfield, Mass.

[73] Assignee: General Electric Company [22] Filed: Aug. 17, 1970 [21] Appl. No.: 64,299

[52] U.S.Cl ..313/325,313/23l,315/35,

[51] lnt.CI. ..H0lj17/00,H0lj21/00 [58] Field olSearch ..3l3/325,23l;

{56] References Cited UNITED STATES PATENTS 3,576,459 4/1971 Sakshaug v.313/325 3,159,765 12/1964 Schultz et al. ..315/35 Primary Examiner-David Schonberg Assistant Examiner-Toby H. Kusmer Attorney-Francis X. Doyle, Valve P. Myles, Frank L. Neuhauser, Oscar B. Waddell and Joseph B. Forman [5 7] ABSTRACT A surge voltage arrester, such as a lightning arrester, is provided with a sparkgap assembly having a plurality of matched pairs of arc-confining chambers that are operable to regulate movement of arcs formed within the chambers of the assembly to prevent the assembly from developing undesirably high peak voltages when a surge voltage is discharged through it, and also to maintain the arc-quenching voltage rating of the assembly at a substantially constant value following repeated surge current discharges. A narrow passageway is provided between each of the matched pairs of arc-confining chambers in order to allow small-current arcs to move between the two chambers while confining large-current arcs to a single one of the chambers, thus, one of the chambers is protected from exposure to destructive erosion and contamination by large-current arcs.

10 Claims, 7 Drawing Figures atented May 16, 1972 2 Sheets-Sheet 1 CURRENT LIMITING SPARKGAP WITH MEANS FOR REGULATING GAP VOLTAGE It is conventional practice in prior art lightning arresters to utilize current limitinggaps connected in series with non linear resistance valve elements to improve the operating characteristics of the arresters. Such current limiting gaps normally employ magnetic means, either in the form of permanent magnets or electromagnets coils, to drive arcs formed in arc-confining chambers of a sparkgap assembly into contact with the arc-stretching and cooling peripheral walls of the arcconfining chambers thereby to accelerate arc extinction and clearing of the assembly. While such current limiting gap assemblies work well for their intended purpose, several problems have been encountered in using them on the high voltage and high current transmission lines that are now coming into more extensive use. As is pointed out in a co-pending US. Pat. application, Ser. No. 801,5 52Sakshaug et al., filed Feb. 24, 1969 issued as US. Pat. No. 3,576,459, and assigned to the assignee of the present invention, these problems have been recognized and various improvements have been developed to cope with them. For example, in the aboveidentified co-pending patent application, there is disclosed a sparkgap assembly for a lightning arrester in which blocking means are provided in the arc-confining chambers of the assembly to retard movement of high-current arcs outward from the sparkgaps in response to the arc-driving motion of the electromagnetic means of the assembly, in a manner such that these high-current arcs are prevented from contacting certain blocked portions of the outer peripheral arc-cooling wall of the arc-confining chambers. Thus, these predetermined partially blocked portions of the arc-cooling walls of the chamber may only be contacted by relatively low-current arcs which are then quickly extinguished by the unheated, and relatively uncontaminated (i.e. not coated with fused arc chamber material) wall portions of the arc-confining chambers.

The present invention is an improvement on the invention disclosed and claimed in the above-identified co-pending patent application and no claim is made herein to any portion of that earlier invention. The present invention affords the desired objectives provided by the invention of the aboveidentified disclosure by utilizing pairs of matched arc-confining chambers in a sparkgap assembly rather than by providing arc movement retarding means within a single arc-confining chamber of an assembly. In addition, the improved structural arrangement of this invention makes it possible to maintain substantially all of one chamber of each matched pair of arcconfining chambers substantially free from contamination by arc-developed particles, such .as molten electrode portions and molten chamber wall materials. Moreover, the present invention provides arc movement regulating means that are automatically operable to minimize the risk of a voltage peak being developed by the assembly if a second surge voltage is applied to it before it has completely cleared a first overvoltage surge; while at the same time maintaining the arc clearing voltage of the arrester at a substantially constant value following repeated discharge operations.

Accordingly, one object of the present invention is to provide an improved sparkgap assembly for a surge voltage arrester in which economically manufactured and ruggedly constructed arc-movement regulating means are incorporated.

Another object of the invention is to provide a sparkgap assembly having a plurality of matched pairs of arc-confining chambers in combination with means for restricting large-current arcs to a first one of the chambers in each of such pairs of chambers, while permitting relatively smaller'current arcs to be moved into the respective second chambers of such pairs of chambers where these smaller-current arcs are extinguished at a substantially uniform voltage. I

A further object of the invention is to provide a sparkgap assembly having a matched pair of arc-confining chambers of a predetermined configuration that is effective to shape largecurrent arcs in the form of a relatively short, peaked loop in one of the chambers, with the peak of the arc loop being directed toward an access passageway to the second of the chambers.

Still another object of the invention is to provide a surge voltage discharge sparkgap assembly having means for automatically regulating gap voltage as a function of discharge current, so an increase in current will quickly result in a switching action within the assembly, which serves to lower gap voltage.

Briefly stated, in one preferred embodiment of the invention, a sparkgap assembly is provided with a plurality of matched pairs of arc-confining chambers and pairs of sparkgap electrodes are mounted in spaced-apart relation within the assembly to form a sparkgap in one of the chambers of each of these matched pairs of chambers. Circuit means are provided to connect the sparkgaps in series and to apply a surge voltage across the gaps thereby causing them to are over. Narrow passageways are formed between each arc-confining chamber of the respective matched pairs of chambers and these passageways are sufficiently small to prevent relatively thick, large current arcs from passing through them from the first chambers containing the sparkgap electrodes to the adjoining second chambers. Thus, when a surge voltage is discharged through the sparkgap assembly, relatively large discharge currents will form arcs that are confined to the first chambers of each pair of chambers, while relatively smallercurrent arcs are allowed to pass through the respective narrow passageways into the second chambers where they are quickly cooled and extinguished against the clean and relatively cool walls of these second chambers. The respective walls of the matched pairs of arc-confining chambers are arranged to protect substantially all of the wall surface of the second, i.e. small-current arc-accepting, chambers from contamination by splattered molten electrode materials or molten arc chamber wall materials that are generated by the high energy, large current arcs confined to the first chambers.

Additional objects and advantages of the invention will become apparent to those skilled in the art when considered in light of the invention as described below, taken in connection with the accompanying drawings, in which:

FIG. I is a side elevation view of a sparkgap assembly embodying a plurality of matched pairs of arc-confining chambers constructed pursuant to the present invention.

FIG. 2 is a top plan view taken along the plane 2-2 of FIG. 1, illustrating the structural arrangement of one matched pair of arc-confining chambers of the assembly depicted in FIG. 1, shown with respect to a large-current arc formed between the electrodes mounted therein.

FIG. 3 is also a top plan view of the matched pair of arc-confining chambers shown in FIG. 2, illustrating a second phase in a normal arc-extinguishing operation of the assembly.

FIG. 4 is still another top plan view of the matched pair of arc-confining chambers depicted in FIGS. 2 and 3, showing a final stage of the arc-extinguishing operation of the invention, in which a relatively small-current arc is illustrated in its extended condition wherein it is in contact with the arc-cooling walls of both arc-confining chambers of the invention.

FIG. 5 is a top plan view of a second embodiment of the invention illustrating a matched pair of arc-confining chambers (including two sub-chambers) that may be used in a sparkgap assembly, similar to that depicted in FIG. I of the drawing, in lieu of the type of arc-confining chambers illustrated in FIGS. 2-4 of the drawing.

FIG. 6 is a side elevation view, taken in cross-section, through one of the pairs of arc-confining chambers of the sparkgap assembly illustrated in FIG. 1, along a plane through the vertical center of this assembly, coextensive with the line (32) shown in FIG. 4.

FIG. 7 is a perspective view of the insulating plate member 3 shown in FIGS. 2-4.

Referring now to FIG. 1 of the drawing, it will be seen that there is shown a sparkgap assembly 1 comprising a plurality of insulating plate members 2, 3, 4, 5, 6 and 7. The insulating plates 2-7 may be of any conventional form and they may be made of any suitable insulating material, for example, some suitable materials are described more fully in U.S. Pat. No. 3,151,273-Stetson et al., filed Dec. 27, 1961 and issued Sept. 29, 1964, which is assigned to the assignee of the present invention. A pair of electrically conductive end plates 8 and 9 are disposed on the top and bottom surfaces respectively of the sparkgap assembly 1. A block of nonlinear resistance valve material 10, such as Thyrite (a General Electric Co. brand of non-linear resistance silicon carbide material), is placed in electrical contact with terminal plate 9 and rests on a third terminal plate 11, which is adapted to be connected by suitable circuit means such as cable 11a, to ground potential. A first circuit means comprising cable 11a and a second cable 8a, that is connected to terminal plate 8, are provided to connect the assembly 1 in operating position to protect a system (not shown) from overvoltage surges, in a manner well understood in the art. It will be understood by those skilled in the art that each adjacent pair of insulating plates 2-7 are formed to define suitable wall means for making arc-confining chambers of predetermined configuration therebetween in any conventional manner well known in the art, for example, such as that disclosed in greater detail in the above-mentioned Stetson et al. patent.

In order to understand the present invention, it is only necessary to realize that each of the arcing chambers formed in the sparkgap assembly 1 is arranged so that matching pairs of arcing chambers are distributed throughout the assembly in a manner that will be described in greater detail below. In one chamber of each pair of chambers there is mounted a pair of horngap electrodes that are operable to move arcs initiated between them outward from the point of arc initiation into contact with arc-confining and cooling surfaces that serve ultimately to extinguish the arcs and clear the sparkgap assembly following a surge voltage discharge. In FIG. 1 of the drawings there is shown, in phantom, four of such electrode pairs 12, 13, 14 and 15, which are electrically connected in series between plates 8 and 9 by a plurality of conducting pins 16, 17, 18, 19, 20 and 21 in a manner well-known in the lightning arrester art. It will also be understood by those skilled in the art, although it is not specifically illustrated in FIG. 1, that the opposite ends of coil 22 are connected, respectively, to pins 18 and 19 so that coil 22 is electrically connected in series with the discharge path formed by the electrodes 12-15 through the sparkgap assembly from terminal plate 8 to terminal plate 9.

In order to fully understand the present invention, it is only necessary to analyze it with respect to a single sparkgap assembly, such as the assembly 1, but it will be understood that in normal practice a plurality of such sparkgap assemblies and associated non-linear valve resistors will be stacked upon each other to form a plurality of series connected assemblies that will have an overall breakdown voltage rating that is directly proportional to the number of such assemblies in the stacked arrangement. Also, as is well known in the art, such a stacked assembly will normally be housed in a suitable insulating housing, which is typically formed of a porcelain cylinder having conductive terminals mounted at its upper and lower ends. For purposes of illustrating the present invention, such a housing is diagrammatically depicted by chain line 23 in FIG. 1.

As described thus far, the particular structural arrangements and combination of elements illustrated in FIG. 1 are relatively conventional and well known in the present development of the lightning arrester art and it will become apparent from the following description that modifications can be made in these elements without affecting the operation of the present invention undesirably if care is taken in the manner described below, pursuant to the invention, to adjust the arc-movement regulating means of the invention to compensate for such modifications of the more conventional elements of a lightning arrester with which it may be associated.

The unique structural features and operating characteristics of the invention will now be discussed in more detail with reference to FIGS. 2, 3 and 4 of the drawing, where there is shown the top surface of insulating plate member 3, whichhas a pair of horngap electrodes 12 and 12a mounted thereon. The electrodes 12 and 12a define a sparkgap 12b between them at their point of closest separation, and a suitable preionizer 24, which may be of any conventional construction, is electrically connected in parallel with a grading resistor 25 across the gap 12b. Any suitable conductive means may be used to form this connection, and as shown in FIGS. 2-4 a pair of electrically conductive straps 26 and 27 are connected between the ends of the preionizer 24 and pins 16 and 17 respectively mounted on electrodes 12a and 12. The upper surface of plate member 3 comprises a generally flat area 28 that has a pair of matched, arc-confining chambers 29 and 30 formed by suitable recessed wall means therein. Means defining a recessed narrow passageway 31 between the first chamber 29 and the second chamber 30 are also provided. Thus, when the plate member 3 is in its assembled position, as shown in FIG. 1, the mating flat bottom surface of insulating plate member 2 cooperates with the generally flat surface area 28 of plate member 3 to essentially seal the upper edges of chambers 29 and 30 so that arcs are confined therein in a manner that will be more fully described below.

It will be understood that a matched pair of arc-confining chambers, similar to the chambers 29 and 30 in configuration, are fonned between each of the adjacent pairs of insulating plate members 3-4, 5-6, and 6-7, so that a total of four main pairs of arc confining chambers are provided in the sparkgap assembly 1, illustrated in FIG. 1 of the drawing. However, in order to understand the principle of the invention, it is only necessary to describe the arc-confining and extinguishing capabilities of one of these matched pairs of chambers. Therefore, the invention will be described with reference to the arcconfining chambers 29 and 30 shown in FIGS. 2-4 of the drawing, in relation to plate member 3. It will be understood that the remaining matched pairs of arc-confining chambers are similar in structure and operate in an equivalent manner in this embodiment of the invention.

As seen in FIGS. 2-4 and as also shown in FIG. 7, the first arc-confining chamber 29 includes means defining a pair of vertical walls 29a and 29b that extend inwardly, respectively from points adjacent the outer ends of the arc-running surfaces of horngap electrodes 12 and 12a. Pursuant to the present invention, these generally straight surfaces of the walls 29a and 29b are arranged at acute angles with respect to a line 32 that extends between the centers of narrow passageway 31 and the sparkgap 12b. This arrangement of the walls 29a and 29b of arc-confining chamber 29 forces any arc formed in the chamber 29 into a loop that peaks at the entrance of passageway 31. In order to illustrate this feature of the invention, a relatively thick, large current arc 33 is illustrated in FIGS. 2 and 3 of the drawing. As can be seen, this are is restricted in its movement outward from the pair of horngap electrodes 12 and 12a by the walls 29a and 29b of chamber 29 so that the arc is prevented from entering the second arc-confining chamber 30. This desirable result is afforded by designing the width of narrow passageway 31 so that only relatively thin, small-current arcs can be forced through it into the second arc-confining chamber 30. Thus, when an over-voltage surge is applied to the second circuit means comprising the series connected sparkgaps and non-linear resistor between ter minal plates 8 and 11, it causes the four main sparkgaps and the coil gap of sparkgap assembly 1 to spark over and form the resultant relatively thick, large current are 33 between the horngap electrodes, such as electrodes 12 and 12a in first arcconfining chamber 29. The thick arc 33 will be confined by the generally straight, arc-cooling surfaces 29a and 29b and their counterparts in the other first chambers of the assembly 1 so that these high energy arcs cannot enter the second arcconfining chambers of their respective matched pairs of chambers. Accordingly, the molten electrode splatter deposits and the melted erosion materials of the walls of the arc-confining chamber 29 are confined almost completely within chamber 29. In addition, although the wall surfaces 29a and 29b of chamber 29 are heated to a molten state in which they develop ionized gases that might cause an arc to restrike after it has once been extinguished, the generally arcuate outer wall portion 33a of the second chamber 30 is not heated to this ionizing condition. Thus, it will maintain its arc-quenching ability during and after arc-extinguishing operations.

To further understand the arc-extinguishing operation of the invention, it should be understood that following the discharge of a large current, relatively thick are, as the current diminishes in size the arc will be forced through passageway 31 into the second arc-confining chamber, in the manner depicted in FIG. 3 by the relatively thin are 34. Such a further lengthening and cooling of the arc quickly raises its voltage and reduces its current so that it becomes thinner and the entire are between electrodes 12 and 12a is rapidly stretched into the position shown by are 34a in FIG. 3. In this position, the are 340 is quickly cooled and extinguished due to a major portion of its length encountering the clean and relatively cool surface 330 of chamber 30, so that the sparkgap assembly 1 can be cleared and rescaled. It will be noted that the second arc-confining chamber 30 comprises a pair of generally straight inner walls 30a and 30b that are arranged to extend respectively from points adjacent opposite sides of the end of the passage 31, that is furthest from the first chamber 29, to points adjacent the ends of the generally arcuate outer wall portion 33a. Also, the inner walls 30a and 30b converge on a plane that extends parallel to the line 32 through the sparkgap 12b and passageway 31 at acute angles that are within the same 90 quadrants with respect to an axis formed by this plane and a line perpendicular to it, as are the generally straight arc-cooling surfaces 29a and 29b of the first chamber 29. This unique arrangement of the inner walls 30a and 30b serves to shield them completely from molten arc-developed particles that may be thrown into the second chamber 30 through the passageway 31 by the burning action of large current arcs such as are 33. Also, in the preferred embodiment of the invention, as it is illustrated in FIG. 4, the generally arcuate outer wall 33a of chamber 30 has a plurality of arcstretching teeth 33a disposed along its periphery and extending into the chamber 30.

It will be noted that the thickness of the insulating material in generally flat surface 28 behind arc-cooling walls 29a and 29b is quite extensive to afford a good heat sink for the large current arcs confined in arc chamber 29. Also, it will be observed that the outer portions of the arc-running surfaces of the electrodes 12 and 12a are spaced away from the respective arc-cooling surfaces 29a and 29b at their closest points thereto a substantially equal distance and this distance is smaller than the width of the passageway 31 between the points 31a and 31b on opposite sides thereof (see FIG. 1) from which the surfaces 29a and 29b, respectively, extend outward. This construction forces the large current are 33 to move its base points on electrodes 12 and 12a rapidly outward along the arcrunning surfaces thereof toward the relatively thick, heat-sink end portions of these electrodes,so that damaging arc erosion of the electrodes is minimized at the relatively thin central portions thereof during operation of the gap. It has been found that this rapid extension of the large current are 33 is facilitated by arranging the generally straight arc-cooling surfaces 29a and 29b substantially parallel to the arc-running surfaces of electrodes 12 and 12a, respectively, in the manner illustrated in the preferred embodiment of the invention shown in FIGS. 2-4.

It should also be noted that the arc-confining surfaces of first chamber 29 are substantially shorter in combined overall length than the arc-confining surfaces of second chamber 30. This arrangement maintains the arc voltage of large current arcs at a desirable low level while allowing relatively smaller current arcs to be quickly raised in voltage to force the sparkgap assembly 1 to clear shortly after the overvoltage surge is discharged through the assembly, thus sharply limiting the amount of power follow current allowed to flow through the assembly 1. In other words, this unique sparkgap structure decreases the ratio of the protective level of the assembly 1 to its reseal level by providing a gap assembly that has a desirably low arc voltage when large current arcs are discharged through it and also has a significantly higher are voltage when smaller, power follow currents are flowing through it. By preventing both large current arcs and the molten by-products of such arcs from entering the second arc-confining chamber 30, this desirable ratio and the arc-extinguishing capability of the assembly 1 is maintained substantially constant after a large number of overvoltage surge currents have been discharged through it.

A very important desirable characteristic of the present invention is that the sparkgap assembly 1 has the ability to automatically adjust its arc voltage in response to an increase in arc current at any stage in an arc elongation operation. Therefore, it a second surge voltage should happen to be applied to the assembly 1 by the secondary circuit means and 11a connected thereto during an overvoltage surge discharge operation of the assembly, i.e. while the assembly is sparked over and is operating to clear a first overvoltage surge, the assembly will automatically adjust its arc voltage to handle the second overvoltage surge without causing a dangerously high voltage peak. If such a condition were to occur in prior art sparkgap assemblies, it very probably would cause a damaging overvoltage to appear on the protected system. However, the present invention prevents such a dangerous overvoltage from occurring, should a second surge voltage be impressed upon the gap assembly before it has cleared a first overvoltage being discharged through it. This desirable mode of operation is so, because if a relatively small, high voltage arc is extended into the second chamber 30, as is are 34a depicted in FIG. 4, when a second overvoltage surge strikes the assembly 1, the resultant increase in current in the arc will cause a thickening of the are which prevents it from passing through the narrow passageway 31 so that a thicker arc, such as the are 33 shown in FIG. 3, will reform across the opening of passageway 31, thus, short-circuiting the extended, higher voltage are and instantly reducing the arc voltage to a safe level. Accordingly, with the unique, dual arc-confining chamber arrangement of my invention, the sparkgap assembly 1 can protect a system from possible damage during a multiple surge situation in which a series of overvoltage surges occur rapidly on the system.

Now that a preferred embodiment of the invention has been described, and its operation discussed in detail, reference is made to FIG. 5 where there is shown a second embodiment of the invention. In this second embodiment of the invention, like identifying reference numerals will be used to indicate component parts similar to those contained in the embodiment of the invention depicted in FIGS. 1-4. Also, it will be understood that while only a single plate member 3 is illustrated in FIG. 5, the general structure of this embodiment of the invention, aside from the particular variations described hereinafter, will be similar to the embodiment of the invention illustrated in FIG. 1. The basic distinction in structure and operation between this second embodiment of the invention and the first embodiment just described is that the second chamber or high voltage arc-confining chamber is basically divided into two sub-chambers rather than being a single chamber such as the chamber 30 of FIGS. 2-4. This distinction and other features of the second embodiment of the invention will become apparent as the description of it proceeds.

Referring now to FIG. 5, it will be seen that the plate member 3 comprises a generally flat insulating surface portion 28 having formed therein a. recessed first arc-confining chamber 29 and a pair of second recessed arc-confining subchambers 30 and 30. Therefore, when a relatively thick, large-current are 33 is moved outward on the arc-running surfaces of electrodes 12 and 12a, it is prevented from entering the second arc sub-chambers 30 and 30' due to the fact that it cannot squeeze through the pair of narrow passageways 31 and 31, substantially in the same manner as the first embodiment of the invention operates. In addition to the fact that the second arc-confining chamber 30 is separated by the wall means 281: and 28b into the pair of sub-chambers 30 and 30, it will be noted that both the first chamber 29 and the second chambers 30 and 30' have generally arcuate outer walls for cooling and quenching arcs forced against them and all of these walls have arc-stretching teeth 29a and 33a, respectively, disposed along their lengths at spaced intervals.

A unique feature of this embodiment of the invention that is important to observe is that the teeth 29a in the first chamber 29 are spaced more closely together than the teeth 30a in the pair of second sub-chambers 30 and 30. As can be seen from the outline of the large current are 33 depicted in FIG. 5, the relatively close spacing of these teeth 29a is effective to prevent large current arcs from being stretched into the spaces between these teeth, therefore, the length and thus the voltage of large current arcs is maintained relatively low. On the other hand, as soon as the large current are diminishes in thickness, when only power follow current flows through it, the resultant thinner arc 34a is rapidly forced into the spaces between the teeth 29a as well as between the teeth 30a in second subchambers 30 and 30'. This arrangement of the relative tooth spacing in the sparkgap chambers 29 and 30-30 in combination with the sub-chamber arrangement of the second arcquenching chamber 30-30, which forces the relatively thin, higher voltage arcs to form at least two extended loops that are positioned respectively in sub-chambers 30 and 30, serves to afford a maximum arc-stretching length in a sparkgap assembly of relatively small outside diameter, so that a high clearing voltage is attainable in combination with a desirably low, large current arc discharge voltage capability.

It is believed that the foregoing description of the embodiments of the invention described herein is sufficient to enable those skilled in the art to practice it successfully. However, in order to supplement this description there is shown in FIG. 6 a cross-sectional view of the sparkgap assembly 1 taken along the line 32 shown in FIG. 4 of the drawing. In this cross-sectional view the plate member 2 and plate member 3 are formed so that the first chamber 29 is approximately twice as high as the second chamber 30, so that large current arcs are not unduly flattened and forced toward the second chamber 30. Also, by maintaining the height of the second chamber 30 relatively small, the upper and lower walls of this chamber are maintained in intimate arc-squeezing contact with a high voltage are forced into it, thus they act with the outer generally arcuate arc-stretching wall of the chamber 30 to cool and quench the arc rapidly.

Those skilled in the lighting arrester art will recognize that additional embodiments and modifications of the invention may be made in light of the disclosure of it herein. Accordingly, it is my intention in the appended claims to encompass all such modifications and embodiments within the scope and spirit ofthese claims.

What I claim and desire to secure by Letters Patent of the United States is:

l. A sparkgap assembly comprising an electrically insulating housing having a plurality of pairs of arc extinguishing chambers therein, each of said pairs of chambers comprising a first chamber and a second chamber and means defining a single narrow passageway therebetween, a plurality of pairs of electrodes, each of said pairs of electrodes being mounted in spaced-apart relationship respectively in one of said first chambers thereby to form a sparkgap in each of said first chambers between the pair of electrodes mounted therein, first circuit means electrically connecting all of said pairs of electrodes in series to form a discharge path including each of said sparkgaps between the endmost electrodes, second circuit means for electrically connecting said endmost electrodes across a voltage source whereby a surge voltage can be applied to said discharge path to sparkover said sparkgaps and form arcs in each of said first chambers, arc driving means for lengthening the arcs formed in said second chambers and for moving said lengthened arcs into said second chambers, said narrow passageways between each of the first and second chambers being operable to prevent arcs in excess of a predetermined thickness from entering said second chambers thereby to cause relatively thick, large current, arcs to be confined to the first chambers, each of said first chambers being arranged with respect to its paired second chamber to prevent a major portion of the molten particles formed by large current arcs in said first chamber from entering said second chambers and to maintain a cool surface area within said second chambers whereby the arc quenching capability of said second chambers is maintained substantially constant during and after the discharge of a plurality of large current arcs through the sparkgap assembly.

2. A sparkgap assembly as defined in claim 1, wherein each of said electrodes includes an arc-running surface, said arcrunning surfaces of each pair of electrodes being arranged to define a horngap that extends outward from the sparkgap formed between the electrodes generally toward the narrow passageway between the first chamber in which the electrodes are mounted to its paired second chamber, each of said first chambers including means defining a pair of walls that extend respectively from points adjacent the outer ends of said arcrunning surfaces, each of said walls including a generally straight arc-cooling surface, said generally straight surfaces being arranged at acute angles with respect to a line extending between said passageway and the sparkgap whereby an are that is forced against said surfaces is formed into a loop that peaks at the entrance of said passageway.

3. A sparkgap assembly as defined in claim 2 wherein the outer portions of said arc-running surfaces on the horngap forming electrodes are spaced away from the respective generally straight arc-cooling surfaces of said walls at their closest points thereto a substantially equal distance, and said substantially equal distance is smaller than the width of said passageway between said points on opposite sides thereof adjacent which said generally straight surfaces extend outward toward the ends of said arc-running surfaces on he electrodes.

4. A sparkgap assembly as defined in claim 2 wherein each of said second chambers includes means defining a generally arcuate outer wall portion and a pair of generally straight inner walls, said inner walls being arranged to extend respectively from points adjacent opposite sides of the end of said passageway furthest from the first chamber to points adjacent the ends of said arcuate outer wall portion.

5. A sparkgap assembly as defined in claim 4 wherein said generally straight inner walls of the second chamber converge on a plane extending through the sparkgap and passageway at acute angles that are within the same quadrants with respect to an axis formed by said plane and a perpendicular line through it as are said generally straight arc-cooling surfaces of said first chamber, whereby said inner walls are shielded from molten, arc-developed particles that are thrown into the second chambers through said passageways and from most of the heating,when large current arcs are formed in the first chambers.

6. A sparkgap assembly as defined in claim 2wherein the arc-cooling surfaces of the first chamber are shorter in combined length than the arc-quenching surfaces of said second chamber.

7. A sparkgap assembly as defined in claim 6 wherein said second chamber includes a generally arcuate outer wall portion having a plurality of arc-stretching teeth disposed along the periphery thereof and extending into the chamber.

8. A sparkgap assembly as defined in claim 1, each of said first and second chambers include means defining generally arcuate walls for cooling and quenching arcs forced against them, the walls in each of said first and second chambers having arc-stretching teeth disposed along the peripheries thereof and extending toward the respective interiors of said chambers, said teeth in the first chambers being spaced substantially closer together than are the teeth in the second chambers, whereby it is easier for an arc of a given size to be forced against the walls between teeth in the second chambers than to be forced against the walls between teeth in the first chambers.

10. A sparkgap assembly as defined in claim 7 wherein said second arc-confining chamber is shorter in vertical height than said first arc-confining chamber, thereby to cause arcs forced into said second chamber to be rapidly cooled due to their contact with the floor and ceiling surfaces of said second chamber. 

1. A sparkgap assembly comprising an electrically insulating housing having a plurality of pairs of arc extinguishing chambers therein, each of said pairs of chambers comprising a first chamber and a second chamber and means defining a single narrow passageway therebetween, a plurality of pairs of electrodes, each of said pairs of electrodes being mounted in spaced-apart relationship respectively in one of said first chambers thereby to form a sparkgap in each of said first chambers between the pair of electrodes mounted therein, first circuit means electrically connecting all of said pairs of electrodes in series to form a discharge path including each of said sparkgaps between the endmost electrodes, second circuit means for electrically connecting said endmost electrodes across a voltage source whereby a surge voltage can be applied to said discharge path to sparkover said sparkgaps and form arcs in each of said first chambers, arc driving means for lengthening the arcs formed in said second chambers and for mOving said lengthened arcs into said second chambers, said narrow passageways between each of the first and second chambers being operable to prevent arcs in excess of a predetermined thickness from entering said second chambers thereby to cause relatively thick, large current, arcs to be confined to the first chambers, each of said first chambers being arranged with respect to its paired second chamber to prevent a major portion of the molten particles formed by large current arcs in said first chamber from entering said second chambers and to maintain a cool surface area within said second chambers whereby the arc quenching capability of said second chambers is maintained substantially constant during and after the discharge of a plurality of large current arcs through the sparkgap assembly.
 2. A sparkgap assembly as defined in claim 1, wherein each of said electrodes includes an arc-running surface, said arc-running surfaces of each pair of electrodes being arranged to define a horngap that extends outward from the sparkgap formed between the electrodes generally toward the narrow passageway between the first chamber in which the electrodes are mounted to its paired second chamber, each of said first chambers including means defining a pair of walls that extend respectively from points adjacent the outer ends of said arc-running surfaces, each of said walls including a generally straight arc-cooling surface, said generally straight surfaces being arranged at acute angles with respect to a line extending between said passageway and the sparkgap whereby an arc that is forced against said surfaces is formed into a loop that peaks at the entrance of said passageway.
 3. A sparkgap assembly as defined in claim 2 wherein the outer portions of said arc-running surfaces on the horngap forming electrodes are spaced away from the respective generally straight arc-cooling surfaces of said walls at their closest points thereto a substantially equal distance, and said substantially equal distance is smaller than the width of said passageway between said points on opposite sides thereof adjacent which said generally straight surfaces extend outward toward the ends of said arc-running surfaces on he electrodes.
 4. A sparkgap assembly as defined in claim 2 wherein each of said second chambers includes means defining a generally arcuate outer wall portion and a pair of generally straight inner walls, said inner walls being arranged to extend respectively from points adjacent opposite sides of the end of said passageway furthest from the first chamber to points adjacent the ends of said arcuate outer wall portion.
 5. A sparkgap assembly as defined in claim 4 wherein said generally straight inner walls of the second chamber converge on a plane extending through the sparkgap and passageway at acute angles that are within the same 90* quadrants with respect to an axis formed by said plane and a perpendicular line through it as are said generally straight arc-cooling surfaces of said first chamber, whereby said inner walls are shielded from molten, arc-developed particles that are thrown into the second chambers through said passageways and from most of the heating,when large current arcs are formed in the first chambers.
 6. A sparkgap assembly as defined in claim 2wherein the arc-cooling surfaces of the first chamber are shorter in combined length than the arc-quenching surfaces of said second chamber.
 7. A sparkgap assembly as defined in claim 6 wherein said second chamber includes a generally arcuate outer wall portion having a plurality of arc-stretching teeth disposed along the periphery thereof and extending into the chamber.
 8. A sparkgap assembly as defined in claim 1, each of said first and second chambers include means defining generally arcuate walls for cooling and quenching arcs forced against them, the walls in each of said first and second chambers having arc-stretching teeth disposed along the peripheries thereof and extending toward the respective interIors of said chambers, said teeth in the first chambers being spaced substantially closer together than are the teeth in the second chambers, whereby it is easier for an arc of a given size to be forced against the walls between teeth in the second chambers than to be forced against the walls between teeth in the first chambers.
 9. A sparkgap assembly as defined in claim 1 including means defining a second narrow passageway between each of said pairs of first and second chambers, and wall means mounted in said second chamber to subdivide it into at least two sub-chambers, whereby an arc forced into said second chamber is forced to form at least two extended loops that are positioned respectively in said sub-chambers.
 10. A sparkgap assembly as defined in claim 7 wherein said second arc-confining chamber is shorter in vertical height than said first arc-confining chamber, thereby to cause arcs forced into said second chamber to be rapidly cooled due to their contact with the floor and ceiling surfaces of said second chamber. 